Earth Plate Tectonics: Vocabulary Terms and Definitions

asthenosphere- the soft, flexible upper layer of the mantle, on which the tectonic plates move

continental drift- the theory that all of Earth’s continents were once joined together into a single large landmass, and then moved apart, forming the continents we see today

convection- transfer of heat by movement of a fluid

convection currents- movement within hot fluids, when the heat source is on the bottom, such as in a boiling pot of soup on the stove. Convection currents happen because the hotter material is less dense and rises; when it reaches the surface, it cools and becomes less dense, so it sinks. This rising and sinking creates a circular motion within the fluid.

convergent plate boundaries- where two tectonic plates move toward each other

divergent plate boundaries- where two tectonic plates move away from each other

Gondwana- the southern continent formed when Pangaea split into two pieces

Laurasia- the northern continent formed when Pangaea split into two pieces

lithosphere- the rigid, brittle layer made up of the crust and the uppermost part of the mantle. It is broken up into pieces called tectonic plates.

mantle convection- convection currents in the mantle that occur because hot rock in the lower part of the mantle is less dense and rises, and cooler rock in the upper part of the mantle cools, becomes more dense, and sinks. Mantle convection is thought to be the mechanism driving the movement of tectonic plates.

mid-ocean ridge- a system of connected underwater mountain ranges that run throughout the world’s oceans. There is a rift valley in the center of the mid-ocean ridge, where magma rises up from the mantle, and pushes out to either side, producing seafloor spreading.

Pangaea- (“all land”) the single huge supercontinent that existed 245 million years ago, when all of Earth’s continents were joined together.

seafloor spreading- the process by which new oceanic crust forms when magma rises up and solidifies at the mid-ocean ridges. The newer crust pushes the older crust out to each side, which is why the age of the sea floor increases with distance away from the mid-ocean ridges.

subduction- the process by which one tectonic plate sinks below another, returning to the mantle, where the rock is re-melted. Subduction takes place at convergent plate boundaries. Oceanic crust, which is denser, will always subduct under the less dense continental crust.

tectonic plates- large pieces of the lithosphere that slowly move on top of the asthenosphere. There are seven primary plates and many smaller ones. The seven primary plates are the African Plate, Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, Pacific Plate, and South American Plate.

tectonic plate boundary- a place where two tectonic plates meet

transform plate boundary- where two tectonic plates slip past each other, moving in opposite directions

For more information on Plate Tectonics, see the USGS publication, This Dynamic Earth